1. Field of the Invention
The present invention relates to an apparatus and a method for punching a workpiece.
2. Description of Related Art
There is known a punching apparatus for making a hole in a workpiece by inserting a punch into the workpiece. Japanese Patent Application Laid-open No. 2003-19698 describes a punching apparatus including two punches. When one of the two punches has been used and worn out at its punching portion, it is switched to the other one. Hence, according to this punching apparatus, the punch changing frequency can be reduced, and the continuous operation time can be prolonged.
Meanwhile, in the punching apparatus described in the above patent document, the punch is supported inside a guide hole formed in a guide member so as to be axially movable. There is a slight clearance between the inner wall of the guide hole and the punch to allow the punch to move in the guide hole. Accordingly, if the punch is inserted into a workpiece in a state of being slightly inclined to the direction vertical to the surface of the workpiece to be punched, it is likely that the circumferential edge of the end surface of the punching portion is abraded more at the side at which the punch is inserted into the workpiece more deeply. Accordingly, if a plurality of holes are punched successively in the workpiece using the punch in this state, the wear may develop rapidly at the end surface of the punching portion of the punch. In this case, there is a concern that, since a large bending moment is applied from the workpiece to the punching portion when the punching portion is inserted into the workpiece, a hole inclined to the direction vertical to the surface of the workpiece may be formed.